The preparation of ketals can be performed without difficulty only by starting from simple ketones, particularly from acetone, and short-chain alcohols by synthesis from the components or by transketalization. However, varying amounts of enol alkyl ethers are always formed, depending upon the structure of the reactants and the reaction conditions. In order to increase the degree of conversion, acid catalysts, molecular sieves or ion exchangers are employed, despite the fact that these compounds are difficult to handle.
Better conversions and higher yields of ketals are achieved by reacting ketones with orthoformic esters, but among the latter only the methyl and ethyl orthoesters can be satisfactorily prepared. Ketals having the complex structure of the formula II below can also be prepared by transketalization from dimethyl ketals, for instance as disclosed in U.S. Pat. No. 3,072,727, which are prepared from 2,2-dimethoxypropane (DMP from acetone). Ketals of the formula II, for example cyclohexanone diisopropyl ketal, are obtained with yields of only 30% (U.S. Pat. No. 3,072,727, Example VI) besides large amounts of various asymmetric ketals. The synthesis with 2,2-dimethoxypropane requires the use of entrainment agents, such as hexane or benzene, but these agents form an azeotrope with 2,2-dimethoxypropane. In claim 1 of U.S. Pat. No. 3,072,727 it is expressly stated that the reaction temperature must not exceed 100.degree. C., because otherwise large amounts of various cyclohexene alkyl ethers are formed.